There is a growing need for accurate and continuous non-invasive monitoring of brain temperature in hospitals and clinics throughout the world. The need for physicians and anesthesiologists to know the brain as well as the core body temperature of a patient is well established. Temperature management of patients under anesthesia during cardio-pulmonary bypass surgery is imperative to a positive outcome and ongoing patient quality of care, yet there is no non-invasive, accurate measurement device available to physicians. Current practice guidelines for anesthesiologists, intensive care physicians, neonatologists, and emergency physicians require the monitoring of the core brain temperature. However, there are no devices that provide immediate, accurate data. Devices that are non-invasive only measure superficial temperatures, insufficient for critical situations. Invasive monitors are placed into the bladder, rectum, esophagus or the nasopharynx to measure core temperature more accurately, but the medical professional must then infer the most important temperature, brain temperature, with the hope that this is accurate enough for critical medical decisions during surgical operations and difficult intensive care unit stays. Thee are several devices that attempt to measure brain temperature. The most accurate prediction of brain temperature today uses intravascular sensors in the pulmonary artery or jugular vein, but these are invasive, inconvenient and potentially harmful. Even sensors directly in the brain have shown that when hypothermia is induced and reversed rapidly, standard monitoring sites fail to reflect cerebral temperature. With success in kidney and bladder temperature detection and monitoring, Thermimage is now developing the AccuTemp Sensor, a non-invasive radiometric based system to accurately and rapidly measure the core brain temperature 5 cm deep. This system consists of a >2.5 cm diameter receiving microwave antenna placed on the patient's forehead, and a specialized radiometer to amplify and process the antenna signal to determine the actual brain temperature. The device detects the energy emitted from the brain at low frequencies with a sensitive receiver that detects signal strength of only a billionth of a watt. There is a clear need for a new, non-invasive temperature measurement device that provides fast and accurate readings of the body's most sensitive tissue, the brain. This Phase II SBIR research and development will demonstrate: 1) the noninvasive sensing technology successfully prepared in Phase I provides reliable monitoring of deep core brain temperature during hypothermic surgery; and 2) the cutting-edge radiometer prototype built in Phase I can be translated into a low-cost system that combines technological innovation with universal commercial appeal and clinical validation.